Fungicide Interval & Never Lose Your Cover
Schedules potatoes
Enter a start date, base interval and a rain or fast-growth reduction to get the effective interval, the number of sprays and every spray date — so cover never lapses.
Plan a fungicide programme
Next: diarise the 4 spray dates and rotate fungicide modes of action (FRAC groups) across them — never repeat the same single-site chemistry back-to-back or resistance builds fast.
Rainfast reduction is a rule of thumb. Real intervals depend on the product's residual, rainfall after spraying, and live disease forecasts — shorten further under prolonged leaf wetness.
Spray interval — key facts
- Protectants
- wash off & need re-spraying
- Base interval
- ≈ 7–14 days (label)
- Heavy rain
- shortens the interval
- Fast growth
- exposes new tissue
- Effective interval
- base − rain/growth reduction
- Schedule gives
- every spray date
- Also
- rotate modes of action
- Privacy
- Runs in your browser; nothing uploaded
Keep the canopy covered before disease gets in
Protectant fungicides only work where they land — they stop spores on the leaf surface but don't move into new growth. So two things steadily break cover: rain washes the deposit off, and fresh leaves and shoots emerge unprotected as the crop grows. Leave the gap too long and a single infection period can let disease in. The answer is a planned interval, tightened when it's wet or growth is fast, so the whole canopy stays protected.
This tool turns that into a calendar — the effective interval, the number of sprays, every spray date and the last spray date from your start date, base interval and a rain or growth reduction. Use it to book sprays in the diary, avoid lapses in cover, and slot in different chemistry for resistance management. Pair it with the Spray Schedule and Pre-Harvest Interval tools for a complete program.
Plan the dates
Lay out every spray from one start date.
Tighten for rain
Shorten the gap when cover washes off.
Cover new growth
Re-spray before fresh tissue is exposed.
Rotate chemistry
Slot in different modes of action per spray.
Frequently Asked Questions
Why do protectant fungicides need re-spraying?+
Protectant fungicides sit on the leaf surface and stop spores germinating; they don't move into new growth. As the crop grows, fresh unprotected tissue appears, and rain and weathering wash the deposit off. So the cover steadily breaks down and the fungicide must be re-applied at a set interval to keep the canopy protected against disease.
How is the spray interval calculated?+
Start from a base interval — the days a protectant lasts under normal conditions — then shorten it for heavy rain and fast growth, which strip cover and expose new tissue. The calculator applies your reduction to give an effective interval, then lays the spray dates out from your start date across the number of sprays needed.
What is the base interval?+
The base interval is how many days a protectant fungicide gives reliable cover under average conditions, often around 7–14 days depending on the product, crop and disease pressure. It's the starting point before adjusting for weather and growth. Always check the product label, since intervals and maximum number of sprays are specified there.
How do rain and fast growth shorten the interval?+
Rain physically washes protectant deposits off the leaf, and rapid growth pushes out new leaves and shoots that were never sprayed. Both leave the crop exposed sooner than the base interval suggests, so the safe gap between sprays shrinks. The reduction you enter captures that, tightening the schedule when conditions are washing-off or growing fast.
What does the calculator give me?+
It returns the effective interval after your reduction, the number of sprays needed, the date of each spray through the period, and the last spray date. That turns a rule of thumb into a clear spray calendar you can put in the diary, so cover never lapses and the whole canopy stays protected.
Is this for protectant or systemic fungicides?+
It's built around protectant (contact) fungicides, which need regular re-application because they don't redistribute into new growth. Systemic and translaminar products move within the plant and can stretch intervals, but they still have label limits and resistance-management rules. Use the interval as a cover-spray guide and always follow the label for systemics.
How does this fit with resistance management?+
Tight, well-timed cover keeps disease pressure low, but you should also rotate fungicide modes of action and respect the maximum number of sprays per product on the label. Use this schedule to plan the timing, then assign different chemistry to the slots so no single mode of action is over-used and resistance doesn't build.
Can I use it for any crop?+
Yes — the interval logic applies to any crop on a protectant program, from potatoes and vines to vegetables and orchards. Enter the base interval and reduction that suit your crop, disease and local advice. High-pressure diseases in wet, fast-growing conditions will naturally produce a tighter schedule with more sprays.
Should I still watch the weather between sprays?+
Absolutely. The schedule is a plan, not a substitute for scouting. Bring a spray forward after unexpected heavy rain, a flush of growth, or a high-risk infection period flagged by a disease model. Use the calendar as the backbone and adjust individual dates as the season actually unfolds.
Are the dates exact?+
They're solid planning dates. Real protection depends on the product, application quality, disease pressure and weather, which the simple reduction can't fully capture. Use the schedule to book sprays and avoid gaps in cover, then fine-tune with scouting and the product label — it's a planner, not a guarantee against disease.